Method and apparatus for making structures of composite material, in particular airplane fuselage sections

RELATED APPLICATION

The present application claims priority to French Application No. 0701241 filed Feb. 21, 2007, which is incorporated herein in its entirety by reference.

FIELD OF THE INVENTION

The present invention relates to a method and a device for manufacturing hollow components out of a composite material, that include a skin, and possibly strengthening elements, and in particular the manufacture of hollow components such as sections of airplane fuselage.

BACKGROUND OF THE INVENTION

Airplane fuselage is conventionally made by assembling fuselage portions of generally cylindrical shape, each portion including a coating or skin and strengthening elements such as stringers, frames, and specific local strengtheners for the subsequent assembly of the wings, cockpit, and landing gear for example.

To limit their weight while guaranteeing good mechanical properties, a proposal has been made for sections made out of composite materials formed of long fibers embedded in a resin matrix, particularly carbon fibers embedded in a thermosetting resin matrix. The composite material skin is conventionally obtained by draping fibers impregnated with unhardened or crude resin over the outer surface of a tool constituted by a rotating male mandrel. The fibers are applied in the form of a strip using a fiber placement head associated with a cartesian displacement system installed around the mandrel. This crude skin, with fibers impregnated with unhardened resin, is then polymerized or hardened in an autoclave oven. The strengthening elements of composite material are manufactured separately from fibers pre-impregnated with resin, then are placed in recesses of the mandrel prior to making the skin by fiber placement. The skin and the strengthening elements in their crude state are then hardened together in the autoclave. The sections thus obtained are of the closed type, with a skin that has, in transverse cross-section, a closed contour extending over 360°.

A manufacturing method of this kind, with a rotating tool, proves particularly tricky to implement. It requires implementation means that are heavy, cumbersome and complex, since the rotated mandrel has to be sufficiently rigid to stop it from bending or to limit its bending.

Furthermore, to obtain a clean outer surface condition, counter-forms, also known as formers, have to be applied against the outer surface of the crude skin for its hardening in the autoclave. These formers with their holding system are long and tedious to install, and increase the weight and volume of the assembly which has to go into the autoclave.

To avoid using formers, U.S. Pat. No. 7,048,024 proposed to make the skin of the sections by applying fibers to the inner surface of a rotating hollow mandrel. The method described only allows the manufacture of the skin of a section, without strengthening elements, and is also based on a rotating tool.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the aforementioned drawbacks by proposing a method for manufacturing hollow components, particularly sections of airplane fuselage, which is simple to implement.

To this end, the present invention proposes a method for manufacturing hollow components out of a composite material, that include a skin, and possibly strengthening elements, said method comprising:

a) inserting a multi-articulated arm fitted with a fiber placement head inside a female mold of elongated shape, said female mold being open via a longitudinal slit intended to receive the support means of said multi-articulated arm,

b) applying fibers, preferably fibers impregnated with resin, to the inner molding surface of the female mold using the fiber placement head to form said composite material skin, said application step being performed by displacement of the application head using the multi-articulated arm and relative displacement in translation of said support means of the multi-articulated arm along said longitudinal slit of the female mold.

According to the invention, the hollow components of composite material are manufactured using a female mold of elongated shape that has a longitudinal slit to allow the displacement of the multi-articulated arm carrying a fiber placement head when making the composite material skin. The method according to the invention allows large dimension hollow components to be made, without a rotating tool.

The female mold has an annular transverse cross-section, the longitudinal slit constitutes a narrow opening that has in transverse cross-section a small dimension relative to the contour of the inner molding surface in cross-section. The female mold may have any type of concave inner surface, with a constant or non-constant transverse cross-section, with or without a longitudinal plane of symmetry. The inner surface is in particular cylindrical and/or truncated cone shaped overall, although concave inner surfaces that include angles between two adjacent plane parts may also be used.

The method according to the invention allows hollow, open, components to be manufactured, that have a narrow longitudinal opening corresponding to the longitudinal slit of the female mold. A hollow component of closed transverse cross-section may easily be made by coupling to the open hollow component obtained a complementary component that has a shape complementary to that of the longitudinal opening. The application step preferably includes the application of fibers impregnated with resin. As a variant, the method includes a dry fiber application step followed by a step of injecting or infusing resin into the dry fibers placed on the female mold.

According to one embodiment, the support means include at least one linear rail for the support and displacement of the multi-articulated arm, and the application step b) is performed on a stationary female mold, by displacement of the multi-articulated arm along the linear rail received in the longitudinal slit of the female mold, said linear rail rests preferably on the ground and the female mold is placed over said rail and rests on the ground on either side of the longitudinal slit.

According to one embodiment, the female mold includes at least one open end where said longitudinal slit emerges, the multi-articulated arm being inserted in step a) through said open end by a relative displacement in longitudinal translation of the support means relative to the female mold.

The method according to the invention may to advantage be applied for making hollow components such as sections of airplane fuselage, that include a skin of overall cylindrical and/or truncated cone shaped cross-section, with at least one longitudinal plane of symmetry. The open hollow components resulting from the method described above constitute open fuselage sections which will subsequently be closed through the assembly of one or more complementary components of composite material complementary in shape to that of the longitudinal openings of the open sections so as to form closed sections. In the case of an airplane fuselage section, said complementary components will constitute to advantage the upper, so-called roof part of the airplane fuselage. This roof part is in fact not much acted upon, and therefore requires few strengthening elements or may be different in structure, for example of a sandwich structure.

Open hollow components of the fuselage section type may also be used to make boat hulls, submarines, space launchers or tanks for example.

According to one embodiment of hollow components of the airplane fuselage section type, the fiber application step b) in order to form the composite material skin is followed by the following steps:

c) installing strengthening elements made out of a composite material in its crude state, inside the female mold, against the skin, such as stringers, frames, and local strengtheners,

d) simultaneous hardening of the skin and strengthening elements for example by putting them in the autoclave oven, and

e) demolding the hollow component of composite material.

To obtain a skin that also has a clean internal surface condition, the method can also include after step c), installing of a male counter-form inside the female mold, against the composite material skin and strengthening elements, this male counter-form being held in place during the hardening step d).

According to one embodiment, the female mold is rigid and the male counter-form is flexible, for example formed of sheet metal in at least two parts that gradually overlap each other, to enable it to be inserted into the female mold in a retracted position and then to be flattened out in a deployed position against the skin.

As a variant, the female mold according to the invention is formed of a flexible female counter-form which is rigidified in a retracted state using stiffeners for the fiber application step. After the have been applied, the stiffeners will be removed to allow it to be fitted onto a rigid male mold.

According to one embodiment, the method includes a step of coupling to the skin a complementary component made out of a composite material, in one or more parts, complementary in shape to that of the longitudinal opening of the skin, so as to form a hollow component of closed transverse cross-section.

In one embodiment, said complementary component is coupled to the hardened skin, after the hardening step d), and possibly after the demolding step e).

In another embodiment, the method includes after step c) positioning a complementary component in its crude state at the longitudinal slit of the female mold, said complementary component being hardened and coupled with the skin during the hardening step d) so as to obtain a closed hollow component.

Another purpose of the present invention is a method for manufacturing airplane fuselage, characterized in that it includes the manufacture of at least two open sections of airplane fuselage as described previously, and the assembly of one or more complementary components of composite material to form closed sections extending over 360°, said complementary components forming the upper part of the fuselage, said complementary components preferably being assembled after the assembly of the open sections via their open ends. This assembly of open sections allows any play between the sections to be easily taken up thereby proving easier to achieve than an assembly of closed sections.

Another objective of the present invention is a device for implementing the methods described previously, characterized in that it includes a multi-articulated arm fitted with a fiber placement head and preferably mounted mobile on at least one linear rail carried on the ground, a female mold including at least one open end and one longitudinal slit emerging on said open end, and holding means able to hold said female mold in a stationary way over said rail in support on the ground over substantially the whole of its length on either side of said rail, such that said multi-articulated arm is able to be displaced inside the mold returning through its open end, said holding means being for example formed by two sole plates of said mold engaged on guide rails anchored to the ground.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood, and other purposes, details, characteristics and advantages will emerge more clearly during the following detailed explanatory description of one particular currently preferred embodiment of the invention, with reference to the appended drawings in which:

<figref idrefs="DRAWINGS">FIG. 1</figref> shows a diagrammatic perspective view of a device for manufacturing hollow components out of a composite material according to the invention, showing the fiber placement system, the female mold, the system for applying a counter-form and the autoclave;

<figref idrefs="DRAWINGS">FIG. 2</figref> a side view of the female mold and placement system in <figref idrefs="DRAWINGS">FIG. 1</figref>, prior to the entry of the robot into the female mold;

<figref idrefs="DRAWINGS">FIG. 3</figref> a front view of the female mold and fiber placement system during the application of fibers to the inner surface of the stationary female mold;

<figref idrefs="DRAWINGS">FIG. 4</figref> shows a perspective view of the female mold during its positioning on the counter-form application system;

<figref idrefs="DRAWINGS">FIG. 5</figref> shows respectively a front view of the counter-form application system positioned in the female mold; and,

<figref idrefs="DRAWINGS">FIG. 6</figref> a partial transverse cross-section view of the female mold with the skin and strengtheners inserted between the counter-form and the female mold.

The figures show a method and a device according to the invention for manufacturing out of a composite material a section of airplane fuselage that includes a skin and strengthening elements. Clearly, the invention may be applied to the manufacture of any hollow component made out of a composite material as described previously.

DETAILED DESCRIPTION OF THE DRAWINGS

With reference to <figref idrefs="DRAWINGS">FIGS. 1 to 3</figref>, the device according to the invention includes a fiber placement system <b>1</b> and a female mold <b>2</b>, as well as an autoclave oven <b>3</b> and an application system <b>5</b> for a counter-form <b>4</b>. The female mold <b>2</b> has an inner molding surface <b>21</b><i>a </i>the shape of which corresponds to that of the skin of the section it is required to make. The inner surface is formed by the inner surface of a substantially continuous wall <b>21</b>, constituted by one or more metal sheets or made out of a composite material, this wall being fitted externally with longitudinal <b>22</b> and transverse <b>23</b> strengtheners to rigidify the female mold. In this embodiment, the female mold is intended for the manufacture of the front section of an airplane fuselage which includes the cockpit part. The inner molding surface <b>21</b><i>a </i>has a so-called rear part <b>210</b><i>a</i>, that is of substantially constant transverse cross-section, generally cylindrical in shape, this front part starting from the rear open and overall circular end <b>24</b> of the mold, and extending via a second so-called front part <b>210</b><i>b</i>, that is of non-constant transverse cross-section, which gets smaller in the direction of the front end <b>25</b> of the mold. In this example, the front end <b>210</b><i>b </i>is truncated cone shaped, with an open front end <b>25</b> of generally circular shape, of radius lower than the rear open end <b>24</b>. By way of example, the radius of the rear end <b>24</b> is of the order of 2 m.

The female mold has a longitudinal slit <b>26</b> extending over the whole length of the mold, from the rear end <b>24</b> to the front end <b>25</b>, to enable the female mold to be positioned over the fiber placement system <b>1</b> as described below.

The fiber placement system includes a multi-articulated arm <b>11</b>, of the six axis robot type, known per se, mounted mobile on a linear axis <b>12</b>, and the end wrist <b>11</b><i>a </i>of which is fitted with a fiber placement head <b>13</b>. The multi-articulated arm displaces the fiber head in all directions. The fiber placement head includes in a known way an application roller <b>131</b> able to come into contact with the mold so as to apply a strip formed of several fibers pre-impregnated with resin. The multi-articulated arm is anchored by its base plate <b>11</b><i>b </i>on a carriage <b>14</b> mounted to slide on the linear axis <b>12</b>, said linear axis being constituted by two parallel rails <b>121</b>, <b>122</b> fixed to the ground. The carriage is fitted with drive means, for example of the motor-driven roller type automatically controlled by a control unit for the displacement of the placement head along these rails. The fibers can be stored on a bobbin on a creel (not shown) and conveyed individually to the application head via flexible conveying tubes, as described in PCT publication W02006/092514, hereby incorporated by reference in its entirety. Furthermore, one or more tension limiting systems as described in this patent document may be provided between the creel and the application head in order to reduce the tension of the fibers at the roller. The creel is also mounted on a following carriage <b>15</b>, mounted on the rails <b>121</b>, <b>122</b>, and for example connected mechanically to the carriage <b>14</b> carrying the robot.

The longitudinal slit <b>26</b> of the mold extends over an angular sector sufficient to enable the rails to be positioned between the two opposite longitudinal edges <b>261</b>, <b>262</b> of said longitudinal slit. The longitudinal slit extends transversely over a small angular sector relative to the angular sector over which the inner molding surface extends. The inner molding surface therefore extends transversely over an angular sector of more than 180°, preferably more than 270°, for example of the order of 300°, as shown in the figures.

The female mold includes two longitudinal sole plates <b>27</b> arranged on either side of the longitudinal slit, by which the mold is supported on the ground on each side of the rails. As shown in the figures, the sole plates rest to advantage on guide rails <b>28</b> arranged on either side of the linear axis <b>12</b>. As a variant, the female mold is fitted with its own displacement system, each sole plate being for example mounted on an autonomous motor-driven carriage controlled by a radio, laser or vision guide and positioning system. The mold rests on the ground over its entire length, which guarantees mold stability and rigidity during the fiber application operations.

To make the skin <b>91</b> of the fuselage section, the female mold is brought over the rails <b>121</b>, <b>122</b> of the fiber placement system by displacing the female mold on the guide rails. The female mold is then immobilized for the fiber application operations. The skin is made by displacing the application head using the multi-articulated arm <b>11</b> and displacing the multi-articulated arm on the rails <b>121</b>, <b>122</b>, along the longitudinal slit of the female mold, the robot being inserted into the mold through the rear open end of the female mold. Once the crude skin has been made, the female mold may be transferred into an autoclave oven <b>3</b> (<figref idrefs="DRAWINGS">FIG. 1</figref>) for hardening by polymerization and/or pressurized reticulation of the skin. The female mold is then removed from the autoclave oven, and the hardened skin is demolded. To do this, the female mold is made in two symmetrical half-molds <b>20</b><i>a</i>, <b>20</b><i>b </i>coupled to each other by their upper part using bolts <b>29</b>. A bond is to advantage positioned at the junction interface of the two half-molds in particular to guarantee the seal during the vacuum forming operation described below.

To advantage, strengthening elements made out of a composite material are placed against the inner surface of the skin to be hardened in the autoclave oven with the skin. In this embodiment, longitudinal sections, usually called stringers, are placed against the inner surface of the skin, over substantially the whole of its length. As can be seen better in <figref idrefs="DRAWINGS">FIG. 6</figref>, the stringers <b>92</b> are of omega-shaped transverse cross-section and are placed on the skin <b>91</b> by inserting a core <b>93</b>, of silicone for example, which will be removed after the hardening operation. Clearly, other types of strengthening elements not shown may be provided, particularly local strengtheners for the front landing gear, the cockpit and the side porthole windows for example.

With reference to <figref idrefs="DRAWINGS">FIGS. 4 to 6</figref>, the device includes a system for the application <b>5</b> of a counter-form or counter-mold for the positioning of a counter-form <b>4</b> against the stringers <b>92</b> and the inner surface of the skin <b>91</b>, so as to hold the stringers against the skin when they are assembled by simultaneous hardening and especially to guarantee a clean inner surface condition for the final section.

The counter-form <b>4</b> is formed of sheet metal complementary in shape to that of the female mold, with a rear part <b>4</b><i>a </i>of cylindrical shape and a front part <b>4</b><i>b </i>of generally truncated cone shape. The counter-form has on its outer surface longitudinal recesses <b>41</b> complementary in shape to that of the stringers. Although not shown for reasons of simplification, the front part <b>4</b><i>b </i>of the counter-form also includes recesses to receive stringers. As shown in <figref idrefs="DRAWINGS">FIG. 6</figref>, the counter-form is formed of sheet metal in several parts <b>40</b><i>a</i>, <b>40</b><i>b </i>with a gradual overlap between two adjacent parts.

The counter-form is placed on the application system <b>5</b> which includes a set of jacks <b>51</b> mounted along a longitudinal support <b>52</b> anchored to the ground to enable the counter-form to be deployed from a retracted position to a deployed position. The counter-form has on its inner surface longitudinal grooves <b>42</b> by which the counter-form comes to be supported against the jack rods.

After making the skin and installing the stringers in the female mold, the female mold is displaced in translation so as to be brought onto the counter-form which is in the retracted position on the application system <b>5</b>, the longitudinal slit of the mold enabling the longitudinal support <b>52</b> of the application system to pass through when it is being fitted. The jacks are then actuated to flatten the counter-form against the skin and the stringers, then the counter-form is coupled to the female mold by appropriate assembly means, placed in particular in the front <b>25</b> and rear <b>24</b> openings of the female mold. The jacks are then retracted, then the female mold with the counter-form are withdrawn from the application system <b>5</b> by an reverse displacement in translation.

Before insertion into the autoclave oven <b>3</b>, a vacuum cover <b>61</b> (<figref idrefs="DRAWINGS">FIG. 6</figref>) known per se, will to advantage be mounted inside the female mold against the counter-form, by inserting a drain felt <b>62</b> to facilitate vacuum formation.

The airplane fuselage will be made in at least two sections. Female molds of specific shape will be provided to make other sections of the fuselage. At least one other specific female mold of non-constant cross-section will be provided to form the rear section of the fuselage, and one or more molds of constant, overall cylindrical, transverse cross-section, will be provided to form intermediate sections. The open sections obtained using female molds according to the invention will then be coupled to each other, in a way known per se, and complementary so-called roof components will be coupled to said open sections.

In an embodiment variant, the carriage <b>14</b> or the base plate <b>11</b><i>b </i>of the multi-articulated arm is of transverse cross-section in the shape of a capital I, the longitudinal slit of the female mold being intended to receive the central part of the I, the lower fin of the I under the female mold and the upper fin inside the female mold. The width of the slit may thus be substantially reduced relative to the embodiment shown. The linear axis <b>12</b> is then embedded in the ground and/or the female mold is raised up relative to ground level.

Although the invention has been described in conjunction with one particular embodiment, it is quite obvious that it is in no way restricted thereto and that it includes all technical equivalents of the means described as well as combinations thereof provided they fall within the framework of the invention.